The present invention relates to a carbon fiber reinforced composite coil spring and the method of making it.
Coil springs have a myriad of uses in all kinds of machinery. They have a number of uses in the automotive industry for vehicle suspension systems and in various parts of the engine (e.g., valve lifter springs). The automotive industry has recently been attempting to reduce vehicle weight in order to lower costs and provide decreased fuel consumption. The substitution of light weight materials (e.g., plastics) for the heavy metals commonly used in automobile parts (e.g., grillwork) is currently one method used to decrease vehicle weight. It would thus be desirable to employ coil springs within automobiles which are comprised of a material which is lighter than the metal currently used in coil springs yet has nearly the same strength and energy storage characteristics.
Metal coil springs are also used within multitudes of industrial machines such as conveyors, compactors, hammers, etc. However, the vibratory capacity and endurance of the metal springs limit the length of time and frequency during which these machines can be operated without requiring replacement of the metal coil springs due to fatigue failure. Fatigue failure occurs in parts which are subjected to continuingly varying stresses, for example, coil springs. The use of a non-metallic material in such springs which could better withstand the repeated vibratory forces is thus highly desirable.
Fiber-reinforced plastic springs have long been known as substitutes for metallic springs, including metallic coil springs. For example, U.S. Pat. Nos. 2,852,424 and 3,378,426 each disclose glass fiber-reinforced plastic coil springs. U.S. Pat. No. 3,142,598 discloses resin-impregnated glass fiber-reinforced automobile leaf springs. In addition, U.S. Pat. No. 3,321,200 discloses a glass fiber-reinforced plastic bellows spring which may be used in vehicle suspension systems. While the use of such glass fiber-reinforced plastic springs provides a low weight substitute for metal springs, the strength of the spring is generally not as high as a comparably sized metal spring. One reason behind the lower strength of fiber-reinforced plastic springs is that randomly oriented non-associated fibers are generally used as the reinforcing medium. Such randomly oriented non-associated or individual fibers have low shear strength and low shear modulus.
It is thus an object of this invention to provide an improved lightweight, fiber-reinforced coil spring.
It is also an object of this invention to provide a carbon fiber-reinforced composite coil spring which exhibits high strength in relation to its weight.
It is further an object of this invention to provide a composite coil spring comprised of resin-impregnated carbon fiber braid which exhibits durability in relation to its weight.
It is yet another object of this invention to provide a method for forming an improved carbon fiber-reinforced composite coil spring.